1. Field of the Invention
This invention relates to a rotary printing press having an inking roller or rollers in rolling engagement with both an ink supply cylinder and a plate cylinder for transferring the ink from the former to the latter. More specifically, the invention pertains to means in such a machine for adjustment of the widths of the nips between the ink supply cylinder and the inking roller or rollers and between the inking roller or rollers and the plate cylinder. The present invention is, however, equally well applicable to a lithographic press, for adjustment of the nip widths of a plate-moistening roller with respect to both a water supply cylinder and a plate cylinder.
2. Description of the Related Art
In rotary printing presses of the type under consideration, the inking roller or rollers are held under pressure against both ink supply cylinder and plate cylinder for positive ink transfer from the former to the latter. The printing ink is conveyed from an ink fountain to the ink supply cylinder via a succession of rollers, while being thereby spread into a thinner, more uniformly thick film, and thence, via the inking roller or rollers of somewhat reduced diameter, onto the printing plate on the plate cylinder. For uniformly inking the printing plate to a required degree, it is essential that the inking roller or rollers be pressed against the ink supply cylinder and the plate cylinder under pressures finely adjusted to provide nips of required widths therebetween.
Out of various suggestions heretofore made for such nip width adjustment, Japanese Patent Publication Nos. 33-3265 and 39-5270 are hereby cited as the prior art closest to the instant invention. According to the former, an inking roller is supported by and between a first pair of swing arms for pivotal motion therewith into and out of rolling engagement with an ink supply cylinder. A second pair of swing arms are coupled to the first pair for moving the inking roller into and out of rolling engagement with the plate cylinder. A dual cam mechanism is provided for independently actuating the two pairs of swing arms, in cooperation with springs biasing the second pair of swing arms toward the plate cylinder.
Upon actuation of the dual cam mechanism so as to increase the width of the nip between inking roller and plate cylinder, for instance, the second pair of swing arms turn in the required direction under the bias of the springs. With such turn of the second pair of swing arms, the first pair of swing arms wholly travel arcuately toward the plate cylinder about the axis of the second pair. At this time, as an inevitable result of the very construction of the dual cam mechanism, the axis of the inking roller is somewhat displaced away from the axis of the ink supply cylinder. Slight as it may be, this displacement of the inking roller axis manifested itself as an unintended change in the nip width between it and the ink supply cylinder.
Another difficulty of this prior art device arose from the fact that the first pair of swing arms have their axis positioned close to the surface of the plate cylinder, so far away from its axis. Consequently, upon actuation of the dual cam mechanism for adjustment of the nip width between inking roller and ink supply cylinder, another unintended change in the nip width occurred with the travel of the inking roller toward and away from the ink supply cylinder.
The adjustment of the nip widths under consideration constitutes an important task of creating an ink film of appropriate, unvarying thickness on the printing plate and so of producing printings of desired constant ink density. The finer and more exact the adjustment, the better will be the quality of the printings. According to the first recited prior art device, however, an adjustment of one nip width affected the other. Optimal adjustment of both nip widths was therefore an extremely difficult job, to be performed only by the most skilled workers. It was equally difficult to maintain proper ink density.
An additional inconvenience resulted from the fact that the inking roller is pressed against the plate cylinder by the force of compression springs acting on the second pair of swing arms. The nip pressure between inking roller and plate cylinder was subject to change, as under the influence of the dynamic balance of the inking roller, particularly during high speed printing. Variations in the nip width could result in changes in ink density on the printing plate and hence in deterioration of the printing quality. Furthermore, the complete prior art device for nip width adjustment was unnecessarily complex and expensive in construction and difficult of manipulation.
The second cited reference, Japanese Patent Publication No. 39-5720, is such that, both interposed between ink supply cylinder and plate cylinder, two inking rollers first have their nip widths with the ink supply cylinder adjusted by angular displacement of eccentric members on sleeves coaxial with the ink supply cylinder. Then the inking rollers have their nip widths with the plate cylinder adjusted without affecting the preadjusted nip widths with the ink supply cylinder, one of the inking rollers by causing, by means of worm gearing, the pivotal motion of a first pair of swing arms supporting the inking roller. The other inking roller is adjusted by turnbuckles capable of acting on a second pair of swing arms supporting the roller.
An objection to this second citation is that the nips are adjustable to required widths only when the nip widths are adjusted in the order of those between inking rollers and ink supply cylinder and then those between inking rollers and plate cylinder. It was totally impossible to adjust only the nip widths between inking rollers and ink supply cylinder without affecting those between inking rollers and plate cylinder. Nip width adjustment during the progress of printing was nearly impossible, either. The control of the ink density was therefore very difficult, and there was a high likelihood of deterioration in printing quality. In terms of mechanical construction, too, this prior art device was just as complex, expensive, and difficult of manipulation as the first described prior art.
The present invention has it as an object to make adjustably variable the width of the nip between an inking roller, or each of two inking rollers, and an ink supply cylinder without affecting the width of the nip between that inking roller and a plate cylinder, thereby making possible the fine readjustment of the rate of ink transfer to the plate cylinder.
Another object of the invention is to make such nip width adjustment possible not only when the printing press is out of operation but when it is printing, too, in order to maintain a high printing quality and to reduce downtime.
A further object of the invention is to make simpler, less expensive, and more easily operable than heretofore the construction of the means for such nip width adjustment.
A still further object of the invention is to make such nip with adjustment possible either manually or by power, and, in the case of power-driven adjustment, either remotely or by direct pushbutton control.
Briefly, and speaking generically, the present invention may be summarized as a rotary printing press having a liquid form roller for receiving a liquid from a liquid supply cylinder and applying the liquid to a plate cylinder. The invention provides, in combination with such means, a first pair of roller support members mounted one adjacent each end of the liquid supply cylinder for angular displacement relative to the same about the axis of the liquid supply cylinder. A second pair of roller support members are mounted respectively to the first pair of roller support members for pivotal motion relative to the same about an axis parallel to the axis of the liquid supply cylinder, the second pair of roller support members rotatably supporting therebetween the liquid form roller for rolling contact with both the liquid supply cylinder and the plate cylinder. Also provided are adjustment means (e.g. adjusting screws) acting between the first and the second pair of roller support members for adjustably causing the pivotal motion of the second pair of roller support members relative to the first pair of roller support members and hence for adjustably varying the width of the nip between the liquid supply cylinder and the liquid form roller.
There are the following positional relationship among the members set forth above: The liquid form roller when in rolling contact with both the liquid supply cylinder and the plate cylinder has its axis substantially contained in a plane containing both the axis of the pivotal motion of the second pair of roller support members relative to the first pair of roller support members and the axis of the plate cylinder. Further the axis of the pivotal motion of the second pair of roller support members relative to the first pair of roller support members is substantially contained in a plane tangent to both the liquid supply cylinder and the liquid form roller at the nip therebetween. Consequently, the width of the nip between the liquid supply cylinder and the liquid form roller is adjustably variable by the adjustment means without substantially varying the width of the nip between the liquid form roller and the plate cylinder.
The foregoing summary contains some generic terms in consideration of the fact that the present invention is applicable to both inking and moistening mechanisms. The word xe2x80x9cliquidxe2x80x9d may therefore mean either ink or water. Further, in the preferred embodiments to be disclosed subsequently, in which the invention is applied to the inking mechanism, the xe2x80x9cliquid form rollerxe2x80x9d will be referred to as inking roller, and the xe2x80x9cliquid supply cylinderxe2x80x9d as ink supply cylinder.
As set forth in the summary above, the nip width between the ink supply cylinder and the inking roller is adjustably variable without substantially varying the nip width between the inking roller and the plate cylinder. The rate of ink transfer from the ink supply cylinder to the plate cylinder is therefore finely readjustable by adjusting screws or the like. Such readjustment is possible during the progress of printing, in order to recover and maintain an optimum ink density on the web.
The adjusting screws may be turned either manually, as in one embodiment, or by power, as in another. The power driving of the adjusting screws, preferably under remote control, is recommended not only for the ease and quickness of readjustment during printing but for the safety of the operator, too.
Both embodiments to be disclosed employ two inking rollers, rather than one, each in rolling engagement with both ink supply cylinder and plate cylinder. Each inking roller is supported essentially alike, and provided with like adjustment means, so that the nip width between each inking roller and the ink supply cylinder is adjustably variable without substantially affecting the nip width between that inking roller and the plate cylinder. Still finer readjustment of ink density is possible in this manner.
Each inking roller requires a minimal number of parts for nip width adjustment with both ink supply cylinder and plate cylinder. All such parts can be compactly mounted within the framework of the press, without making the same any larger than heretofore.
The above and other objects, features and advantages of this invention will become more apparent, and the invention itself will best be understood, from a study of the following description and appended claims, with reference had to the attached drawings showing the preferred embodiments of the invention.